This invention relates to a built-in zero sequence ground fault indicator for a bolted-pressure contact switch.
Fused load-break switches are frequently used as service entrance equipment and in other relatively high current applications. Typically, multi-pole switches of this kind may be required to interrupt currents of 400 to 4,000 amperes. Most switches of this kind are provided with positive pressure-applying mechanisms for assuring good contact between the switch terminals. The contacts of these switches are opened and closed rapidly to minimize arcing and thereby avoid pitting and deterioration of the switch contacts. Rapid opening and closing of the switch contacts have been accomplished by the use of an over center spring drive. The spring drive can be energized and the switch actuated by manual or electrical means. The manual or electrical means is not used directly to open or close the switch contacts but instead operates a trip mechanism to release the spring drive. Switches of this type have also been equipped with electrical means such as electrical motors or solenoids to actuate the switch and energize the spring drive, thereby permitting remote operation of the switch.
In order to sense low level ground faults, bolted-pressure contact switches have been equipped with ground fault sensing mechanisms. However, this has required that the terminals of the switch be extended to accomodate the sensor and has also necessitated rearrangement of the bus bars. For these reasons, standard housings for bolted-pressure contact switches have not been usable with ground fault sensing without extensive modification of the switch housings.